Near the railroad tracks on the outskirts of Flint, Mich., there is an old pump house, the walls of which have long served as a kind of communal billboard. The Block, people call it. People paint messages there — birthday wishes, memorials for the dead. In January, after Gov. Rick Snyder declared a state of emergency in response to Flint’s water crisis, a new message appeared, addressed implicitly to Snyder but also to the world: YOU WANT OUR TRUST??? WE WANT VA TECH!!! In the history of political graffiti, “We want Va. Tech” may sound like one of the least stirring demands ever spray-­painted on a wall, but in the context of Flint, it was charged with the emotion and meaning of a rallying cry.

By “Va. Tech,” the message’s author meant a Virginia Tech professor of civil and environmental engineering, Marc Edwards. Edwards has spent most of his career studying the aging waterworks of America, publishing the sort of papers that specialists admire and the rest of us ignore, on subjects like “ozone-­induced particle destabilization” or the “role of temperature and pH in Cu(OH)₂ solubility.” Explaining his research to laypeople, he sometimes describes it as “the C.S.I. of plumbing.” Edwards is a detective with a research lab and a Ph.D. In 2000, after homeowners in suburban Maryland began reporting “pinhole leaks” in their copper pipes, the water authority there brought in Edwards. In 2002, after receiving a report that water in a Maui neighborhood had mysteriously turned blue and was giving people rashes, Edwards took on the case.

Until last year, the most famous case Edwards investigated was the lead contamination of the water supply in the nation’s capital — still the worst such event in modern American history, in magnitude and duration. In Washington, lead levels shot up in 2001, and in some neighborhoods they remained dangerously elevated until 2010. Edwards maintains, and spent years working to prove, that scientific misconduct at the Environmental Protection Agency and the Centers for Disease Control and Prevention exacerbated the D.C. crisis. A congressional investigation culminated in a 2010 report, titled “A Public Health Tragedy: How Flawed C.D.C. Data and Faulty Assumptions Endangered Children’s Health in the Nation’s Capital.” It confirmed many of his allegations, but the experience was for Edwards a decade-­long ordeal that turned him into a reluctant activist — or as he prefers to say, “a troublemaker.”

For television appearances, Edwards will put on a suit and tie, and the tie almost always bears a picture of some endangered animal: a giant panda, for instance, or a water buffalo. But on the morning we met, in his lab at Virginia Tech, he was dressed in a black track suit and a pair of running shoes — the uniform he prefers. At 52, he has the youthful yet slightly skeletal good looks of an avid long-­distance runner, which he is. “Before Flint, I was running 50 miles a week,” he told me. “Now I’m down to 27.” Running keeps him sane, he says, or at least saner than he would be otherwise. More than once during his investigations into D.C. and Flint, he wondered if he might be losing his mind.

“Before D.C.,” he told me, “I think I was a normal professor.” In the sciences, normal professors with tenure do not maintain websites on which they publish incriminating emails obtained under the Freedom of Information Act. Or habitually refer to unethical bureaucrats as “pathological lying scumbags.” Or allude frequently to Orwell’s “1984,” Arendt’s “The Origins of Totalitarianism” and Ibsen’s “An Enemy of the People,” an 1882 political drama about polluted water contaminating the profitable baths in a Norwegian town. Of his fellow tenured scientists, a normal professor doesn’t say things like, “We are the greatest generation of cowards in history.”

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The poisoning of Flint can be traced to the moment on April 25, 2014, when, with the push of a button, the city stopped buying treated water from Detroit and began drinking from its own notoriously polluted river. In the year after the switch, the city violated the Safe Drinking Water Act four times — for increases in E. coli, coliform bacteria and trihalomethanes, a class of carcinogenic “disinfection byproducts.” The switch also probably contributed to an outbreak of Legionnaires’ disease that has killed at least 12 people. And for reasons that are still in dispute and under investigation, workers at Flint’s hastily refurbished and understaffed treatment plant failed to add corrosion inhibitors, chemicals that coat the interior of pipes, providing a prophylactic barrier. Stop adding them, and the coating wears away, the pipes corrode, lead leaches into the water.

Edwards himself didn’t discover the corrosive chemistry of Flint’s water. LeeAnne Walters, a mother of four, did that after her children broke out in rashes. In early 2015, Walters began investigating. A test conducted by the city at her request detected dangerously elevated lead levels in her tap water. After obtaining the list of chemical ingredients that the Flint treatment plant was using, Walters shared them with an E.P.A. drinking-­water expert named Miguel Del Toral. Notably absent from the list: corrosion inhibitors. “I couldn’t believe that they didn’t have corrosion control,” Del Toral told me. Untreated, nearly all water will corrode metal, but some water sources are more corrosive than others, and the water from the Flint River, Del Toral says, “was corrosive as hell.” He had corresponded with Edwards before; now he had Walters collect water samples from her house and send them to Edwards’s lab for analysis. In one sample, the lead levels were so high that the water qualified as hazardous waste.

Last summer, when Walters went public with an E.P.A. memorandum that Del Toral wrote and sent her, the Michigan Department of Environmental Quality tried to discredit it. In statements to reporters, a department spokesman, Brad Wurfel, called Del Toral “a rogue employee” and said Michigan officials had found no evidence of a citywide lead contamination. Wurfel’s advice to Flint residents: “Relax.” Walters, whose son had already received a diagnosis of lead poisoning, enlisted Edwards, who began conducting, with the help of Walters and other volunteers, what he claims was “the most thorough independent evaluation of water in U.S. history.”

Last September, at a news conference on the lawn of City Hall, encircled by activists, Walters by his side, Edwards announced what he had found: that lead levels in the tap water of “about 5,000 Flint homes” exceeded the safety standard — 10 parts per billion — of the World Health Organization. In October, the city switched back to Detroit water. In December, Flint’s newly elected mayor, Karen Weaver, presented Edwards with a commemorative plaque. “We had cried out for a year and a half, and it wasn’t until you came that you gave our voice some validation,” she told him. “It wasn’t until you came, and we got those Virginia Tech results, that we knew: People couldn’t say we were crazy. They couldn’t say we didn’t know what we were talking about. They couldn’t say it was our imagination.”

Edwards’s decision to champion the cause of activists is not one scientists typically make; they avoid political controversies for a reason. In 2011 the American Association for the Advancement of Science, the largest scientific society in the world, commissioned a paper on the “standards, benefits and risks” of advocacy. “When scientists become advocates, they become ‘partisans’ and are no longer neutral conveyors of scientific information,” the paper stated. “While the line between neutral and partisan, between dispassionate and passionate, is not easily drawn, it nonetheless exists.” Scientists who transgress that line tend to have their credibility impugned. Just ask the climatologists. Or think of Rachel Carson, who was a scientist with the United States Fish and Wildlife Service before she became an author. Upon the publication of “Silent Spring” in 1962, critics accused her of hysteria and Communism.

Consider the case of Clair Cameron Patterson, the geochemist who first determined the age of the planet from lead isotopic data. While working with that data, Patterson discovered, in the early 1960s, that scientists had grossly underestimated the amount of lead we were adding to the environment. There was lead in our gasoline, in our paint, in canned tuna, in our plumbing. The lead levels in the bodies of postwar Americans were 700 to 1,200 times as high as those of their preindustrial ancestors, Patterson estimated. For more than 20 years, the lead industry resisted his campaign to ban the metal from consumer products. The United States didn’t remove the last of the lead from gasoline until 1996. Though our lead levels are still around 10 to 100 times as high as those of our preindustrial ancestors, they have, on average, been coming down ever since. But in 1965, when Patterson first began sounding the alarm about lead, prominent toxicologists dismissed him as a “zealot” who had abandoned science for “rabble rousing.”

Edwards considers Patterson a role model. He would prefer to remain dispassionate, he says, but his experiences in D.C. and Flint taught him that neutrality carries its own risks. If, as surveys suggest, Americans are less willing to defer to the authority of scientific experts than they once were, scientists themselves are partly to blame, Edwards believes. In the academy, competition over a dwindling pool of funding and the pressure to publish have created “perverse incentives,” he said in a recent interview with The Chronicle of Higher Education. As a result, “the idea of science as a public good is being lost,” and along with it, the “symbiotic relationship” between the scientific community and the public. For him, his intervention in Flint was a kind of demonstration project, a case study of how to conduct science ethically, in the public sphere and for the public good.

Michigan officials initially tried to discredit him, too, trotting out the rabble-­rousing charge. Although the state “appreciates academic participation in this discussion,” Wurfel, the Michigan Department of Environmental Quality spokesman, wrote in an email to a local reporter last September, “offering broad, dire public-­health advice based on some quick testing could be seen as fanning political flames irresponsibly.”

A scientist abiding the paper commissioned by the American Association for the Advancement of Science would have responded to Wurfel dispassionately, perhaps by conveying his data in a peer-reviewed journal. Instead, Edwards fought back like some 21st-­century pamphleteer. On a website one of his graduate students built, flint​water​study​.org, he ­posted, along with incriminating documents and helpful tips for Flint residents, acerbic commentaries condemning Wurfel and other officials he considered culpable. “You wish they’d listen to reason, scientific facts, the truth,” he told me. “But if they’re corrupt, the only weapon you’ve got is ridicule.”

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A Flint resident’s car being loaded with bottled water in August.Credit
Jeremy M. Lange for The New York Times

In Flint, Edwards’s pugilistic brand of advocacy seemed to work. Last winter, Wurfel and other officials resigned. In February, Congress invited Edwards to testify at hearings devoted to the Flint crisis, and in a rare display of bipartisanship, Democrats and Republicans alike solicited his opinions not only on matters of science but also on matters of policy and morality and the law, treating him as a sort of oracle or ombudsman. It was hard to recall a scientist who had received a warmer reception on Capitol Hill. Gov. Rick Snyder had by then acceded to the demand spray-­painted on the Block, appointing Edwards to the task force overseeing the state’s response to the emergency in Flint. The E.P.A. awarded Virginia Tech an $80,000 grant to retest the city’s water. Edwards had done as much as anyone to expose the betrayal of public trust in Flint. Who better than him to restore it?

With his son and daughter, both teenagers, and his wife, Jui-Ling, Edwards lives at the border of a national forest, atop Brush Mountain, one serration in the Appalachian chain. They heat their three-­story house entirely with firewood that Edwards scavenges from the forest, and they draw their water from a well. Throughout the house, Edwards keeps gym equipment strategically placed — dumbbells in his living room, a treadmill and barbells in the basement.

He grew up in Ripley, N.Y., a rural town on the shore of Lake Erie. As a teenager, he worked menial jobs, picking grapes in the local vineyards and cleaning rooms at a motel, saving for college. He attended SUNY-­Buffalo, majoring in biophysics because it was reputed to be the hardest major, combining the curriculums of biology, physics, chemistry and math. In his senior year, he applied successfully to the graduate program in civil engineering at the University of Washington, in Seattle. In his application’s personal statement, he wrote that the restoration of Lake Erie, which he witnessed in the 1970s after the passage of the Clean Water Act, had given him his life’s purpose: to improve “the future of water supplies.”

The director of his dissertation at U.W. was an environmental engineer named Mark Benjamin. The two grew close, and have remained close, despite differences of temperament and politics. In the acknowledgments section of his dissertation, Edwards says of Benjamin, “I will do well to follow his sterling example in future professional activities, while at the same time attempting to shake the aftereffects of his Stanford socialistic drivel.”

“As you probably know, since you’ve spent a lot of time with him, Marc has strong political views,” Benjamin told me. It was true. Edwards had made his political views clear. In Virginia, when I visited him in February, we had watched the returns of the South Carolina presidential primaries together in his living room, Edwards in gym shorts lifting 27-pound weights. He is a Republican, a fiscal conservative with a libertarian bent, as well as an environmental-­justice warrior. “The crack about ‘Stanford socialistic drivel’ had become a running joke by then,” Benjamin says. “But absolutely there was more than a grain of serious resentment at people feeling entitled by having gone to the best schools, as the world sees those rankings. Given his SUNY-­Buffalo background, I’m sure he felt disrespected.”

Edwards and Benjamin believe that, adhered to rigorously, the scientific method provides some protection from bias, political or otherwise, and by all accounts Edwards is a brilliant scientist. “Really, he’s almost unique in the field right now, how much he’s admired,” Benjamin says. Other scientists I spoke to said the same, affirming the wisdom of the judges who in 2007 awarded Edwards a MacArthur Fellowship, the so-­called Genius Grant. (In its citation, the foundation praised him for “playing a vital role in ensuring the safety of drinking water.”)

Outside the realm of science, Edwards has strong differences of opinion with many of his admirers. In the written statement he submitted with his congressional testimony in February, he included a somewhat cryptic sentence. “While misconduct has always been a problem, at some level, since the earliest days of the scientific revolution,” he wrote, “the rise of institutional scientific misconduct is a relatively new phenomenon.”

When I asked him what he meant, he referred me to a 2014 book for which he wrote the foreword, “Science for Sale,” by David L. Lewis, an E.P.A. whistle-­blower. Lewis defines “institutional scientific misconduct” as “the fraudulent manipulation of science by government agencies, corporations and academic institutions to support government policies and industry practices.” In his foreword, Edwards commends Lewis but quibbles with his definition. It’s the misconduct of public institutions, not private ones, that worries Edwards most. “In my opinion,” he writes, “the abuses and dangers of institutional scientific misconduct,” where no profit motive appears, “far exceed those arising from misconduct in industrial science.”

Edwards’s cynicism about the public sector was deeply shaped by the “D.C. saga,” Benjamin told me. In Washington, when Edwards started leveling allegations against the E.P.A. and the C.D.C., he was treated by some as a pariah in his field, the scientist who cried “Lead!” in a crowded metropolis — or “the engineering equivalent,” Benjamin says, “of an ambulance chaser.”

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A rusted lead water pipe from Edwards’s work on the water crisis in Washington.Credit
Jeremy M. Lange for The New York Times

Bruce Lanphear, a public-­health physician who has studied environmental lead poisoning since the 1990s, shares Edwards’s concern about the failures of regulatory agencies but attributes them mainly to the institution that invited Edwards to testify: Congress. He pointed out that in the last two decades Congress has cut the E.P.A.’s budget by 30 percent, even as the agency’s regulatory mandates have increased.

“We’re still using children as biological indicators for substandard housing,” Lanphear says. “Everything is focused on short-term solutions, crisis thinking, the bottom line.” The crisis in Flint has led to congressional hearings and criminal charges against nine Michigan officials but not yet to the kind of action Lanphear believes the nation needs to take. “Within the next 30 years, we’re going to need to have replaced our entire water infrastructure,” Lanphear says. “So what’s the plan?”

This winter and spring, whenever Edwards went to Michigan, television cameras tended to follow. One morning, a team sent by RT, the Russian news network, trailed him to an elementary school — not in Flint but just outside it, in the comparatively affluent, majority-­white suburb Grand Blanc. Joining Edwards on his classroom visit was Mona Hanna-­Attisha, a pediatrician at Hurley Medical Center in Flint. Like many people in Michigan, she first heard of Edwards last summer. At the time, she was working on a study of her own, an analysis of pediatric blood data that would confirm what the Virginia Tech water study had implied — that blood-lead levels in Flint had shot up after the city seceded from Detroit’s water system. Edwards had identified the cause, Hanna-­Attisha the effect. She wasn’t sure why state agencies had missed the blood-lead increase she had found. Trying to explain their failure, their collective blindness, she mentioned an aphorism she learned in medical school: “The eyes don’t see what the mind doesn’t know.”

In a second-­floor classroom, the pair sat in tiny red chairs, Edwards in an ill-­fitting suit, Hanna-­Attisha in an ankle-­length parka, drinking cocoa from mugs and taking questions from small interrogators — the fourth-­grade version of a congressional hearing. Edwards testified that something “governments don’t do very well is fix the problems they create.”

“Do you blame the government for what happened?” a boy in the front row asked.

“Yes, I do,” Edwards said. “Did you pick up on that?”

Another child wanted to know what happens to officials who break the law.

Grand Blanc and Flint have a tangled history. A half-­century ago, during the days of white flight, General Motors executives pushed to combine suburbs and city into a single metropolis — New Flint — with shared government services and a shared tax base. In 1958, opponents in the suburbs blocked the plan. People in parts of Flint now have a life expectancy 15 years lower than those in some neighboring suburbs, and even before the water crisis, children in Flint had higher blood-lead levels than their suburban counterparts. “Our Flint kids have every obstacle to success,” Hanna-­Attisha told me back at her office. “We have a 42 percent poverty rate here; it’s about 16 percent in the state. We have one of the highest crime rates. We don’t have full-­service grocery stores.”

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Edwards unloading water samples from Flint at his laboratory at Virginia Tech in June.Credit
Jeremy M. Lange for The New York Times

Flint’s plight, in other words, predated the water crisis and will outlast it. At the time of Edwards’s classroom visit, four months after Flint rejoined Detroit’s water system, Edwards’s research team and the citizen scientists who volunteered to assist it were preparing to resample the same 271 taps that Virginia Tech sampled last summer. The results would reveal how far lead levels had fallen. Knocking on doors, they encountered an unanticipated obstacle: Many of the occupants of those 271 homes had moved away, locking their doors behind them. Civil engineers refer to the time that water spends in pipes as “water age.” Flint’s loss of population meant that fewer people were opening their taps, which meant that Flint’s water was getting older. The older the water, the longer it would take for corrosion inhibitors to work their way through all the pipes.

Of the 271 homes that Virginia Tech tested last summer, the lead levels in Elnora Carthan’s house — 1,050 parts per billion, 70 times as high as the E.P.A. limit — were the highest. When Edwards visited Carthan’s tiny yellow bungalow in the spring, scraps of copper piping lay coiled in the grass, the remnants of the service line that a construction crew sent by the city had just ripped out. The crew was still there, putting a new copper service line in, threading it under the asphalt to the water main across the street.

“It’s a big C.S.I.-­of-­plumbing case,” Edwards said, “because why does she have so much lead but no lead pipe?” He crouched on the lawn, peered into a length of pipe and blew into one end of it. Having found no clues, he tagged a few scraps to take back to his lab for further study.

In Carthan’s basement, he inspected the plumbing with a flashlight. Traditionally, civil engineers have concerned themselves with public works, leaving household plumbing to plumbers. But in the 1990s, Edwards realized that the distinction between private property and public works had everything to do with legal liabilities and nothing to do with chemistry. Legally, a homeowner is responsible for what happens after water crosses the property line, which is one reason water companies are keen to attribute lead poisoning to household sources. But what happens to water at the municipal treatment plant, or on its subterranean journey, can have unintended side effects within the home. Depending on its chemistry, water can eat pinholes into copper pipes. It can turn a basement water heater into an incubator of legionella or other bacteria. And if its chemistry is corrosive, it can leach lead from the solder or from brass faucets. Old plumbing fixtures made of brass were often as much as 20 percent lead by weight, and until 2014 even brass faucets advertised as lead-free could contain up to 8 percent lead by weight in the United States. Solder, brass fixtures or maybe a chunk of lead obstructing a pipe — those, Edwards hypothesized, were the likely sources of the lead in Carthan’s water. To test his hypothesis, he hired a local plumber for the day to replumb Carthan’s house with PVC. From her old plumbing, he collected samples and added them to the heap of evidence destined for his lab.

Out in her driveway, Carthan stood by, watching the scientists at work. Born in Arkansas, she moved to Flint in 1976 and had been there ever since, even though her children and grandchildren had all moved away. She herself had never drunk the poisoned water or served it to guests. “When they first switched,” she said, “it had an odd smell. A really odd smell. You knew something was wrong. You turn the shower on, and you could smell it. You take a shower, five or 10 minutes later, you begin to itch. You knew there was something wrong. That’s why people were complaining. But nobody was listening” — until Virginia Tech arrived. Carthan signed up to participate in last summer’s water study as soon as she heard about it.

Edwards credited much of the success of his intervention in Flint to an anthropologist named Yanna Lambrinidou. Lambrinidou had helped organize a coalition of activists during D.C.’s lead crisis. It was their work, and Lambrinidou’s in particular, that brought his D.C. research to the attention of Congress, Edwards told me. Without her efforts, the congressional investigation that vindicated him might never have happened.

Collaborating on the D.C. crisis, Edwards tutored Lambrinidou in the chemistry of lead corrosion. In turn, she taught him about the value of “vernacular” knowledge and the ethical hazards of scientific hubris. For several years, Edwards and Lambrinidou together taught a course at Virginia Tech called Engineering Ethics and the Public, in which students studied cases of scientific misconduct and practiced ethnographic methods — what Lambrinidou calls “learning to listen.” In Flint, Edwards told me, he tried to apply everything he had learned from her.

Lambrinidou was at first reluctant to speak to me. Eventually, she explained why. Although she considered “Marc’s contribution in Flint and D.C. absolutely essential,” on his website and in the news media, Edwards had contributed to a simplistic “hero narrative” about Flint. This was a complaint I heard from other environmental-­justice advocates — that Edwards had cast himself, or been cast by the news media, as Flint’s white knight. A number of people I spoke to, Lambrinidou among them, referred to a comment that Irma Muñoz, the president of an advocacy group called Mujeres de la Tierra, had made at a recent conference on citizen science: “We don’t want our day saved,” Muñoz said. “We want to save our own day.”

Paul Schwartz, a water activist who worked with Edwards and Lambrinidou in D.C., told me there were times when Edwards “would be helpful and supportive, and there were times when he shoved us aside and inserted himself right into the middle of the story.”

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A sign for water-filter distribution in Flint.Credit
Jeremy M. Lange for The New York Times

In an email to me, Lambrinidou wrote: “We are all capable of outstanding courage (even if at times we have been ‘cowards’) and of outstanding wrongdoing (even if at times we have been ‘heroes’). This is what it means to be human, no? This is what it means to be a parent, a teacher, a doctor, a president. We all know that at times we’ve shined beyond even our own greatest expectations, and at times we’ve failed spectacularly to the point of self-shock. I think that Marc, not unlike many individuals and institutions embracing ‘hero’ narratives, struggles sometimes to hear this.”

She described an alternative situation that might have played out in Flint, one she had seen play out in other collaborations between citizens and scientists. What if Edwards had stayed in Virginia, or at least away from the cameras? What if he had supported the activists in Flint with technical expertise but let them announce the findings of the study they conducted with his help? I wasn’t sure. If LeeAnne Walters had presented the evidence on the lawn of City Hall last September, would people outside Flint have taken the evidence as seriously?

This spring, a new outsider began making trouble in Flint, the actor Mark Ruffalo, who founded an environmental group called Water Defense. Ruffalo had appointed a man named Scott Smith to serve as Water Defense’s chief water scientist. When Smith went to Flint, he took what he called Water Defense Waterbugs, colorful sponges of “open-­cell elastomeric foam technology.” They looked like Koosh balls made from shredded swimming-­pool noodles. Smith tossed them into the Flint River. He tossed them into bathtubs and shower stalls. In a video that Water Defense posted online, Smith claimed that the research carried out by others was fundamentally flawed, because it relied entirely on “grab samples” that collect “a split second” of water, and people don’t “bathe for a split second.” (In fact, Edwards says, Virginia Tech used an array of proven sampling methods.)

In April, at a meeting of the Flint City Council inside City Hall, Smith issued a warning that bore an uncanny resemblance to those Edwards issued last September. “It is irresponsible and incomprehensible for anyone to declare or suggest that the water in Flint is safe to bathe or shower in,” Smith said. No one had tested the showers and bathtubs of Flint for “the full spectrum of chemicals, including but not limited to chemicals that volatilize or aerosolize in the air and pose a direct inhalation risk into the lungs.” It was a convincing performance, not only because Smith sounded scientific but also because his assessment helped explain symptoms that residents of Flint continued to report even after they stopped drinking the poisoned water — rashes, hair loss, difficulty breathing, a burning in the lungs. In February alone, there were so many complaints from Flint residents that state and federal public-­health officials opened a new investigation. (Asked to comment for this article, the C.D.C. said that “results from the investigation have not yet been released.”)

“This is exactly the danger of having untrustworthy government science,” Edwards wrote me in an email in May. “A Hollywood fraud rolls into town, and they cannot even call him out.” Concerned that Water Defense would scare even Flint residents who reported no adverse symptoms, he decided to go after Ruffalo and Smith the way he went after government officials last fall. “A-List Actor but F-List Scientist: Mark Ruffalo Brings Fear and Misinformation to Flint” read the headline of a blog post he published on flint​water​study​.org.

“Not everyone who challenges the claims of the E.P.A., C.D.C. and State of Michigan are automatically correct,” he wrote. Smith had no degrees in the sciences, Edwards noted, and appeared to be a businessman of dubious accomplishment who was now trying to market his sponges. Edwards made the case that Water Defense’s meddling would do harm. A recent increase in gastrointestinal infections in Flint, Edwards speculated, could have been caused by the poor hygiene that Smith’s “fear-­mongering” had encouraged. The disinfection byproducts, or DBPs, that Water Defense had detected in showers — produced by reactions between chlorine and organic matter — had been reviewed by a scientist Edwards recruited, Dr. David Reckhow of the University of Massachusetts, Amherst, “one of the foremost authorities on DBPs in the world.” Reckhow’s assessment: “There is nothing at all unusual or abnormal in the Flint DBP data.”

Water Defense, though, made its own appeal to authority. Smith was not a credentialed scientist, it was true, but all his samples were being tested by an independent lab and reviewed by Judith Zelikoff, a toxicologist in the environmental-­medicine department at New York University. (Water Defense is “producing data in an ethical and transparent manner,” Zelikoff told me, “and I will continue to support them.”) Once again, Flint residents were left to wonder whom to believe.

This time, Edwards’s pugilistic brand of advocacy proved less effective than it had last fall. Among the activists who fought to expose Flint’s water crisis, a schism emerged. There were those, led by LeeAnne Walters, who kept faith in Virginia Tech, and those, led by another Flint mother, Melissa Mays, who placed their trust in Water Defense. Mays helped conduct the fieldwork for the Virginia Tech water study and, like LeeAnne Walters, she appeared alongside Edwards at his news conference last September. Now, after his denunciation of Water Defense, she renounced him. “You aren’t listening anymore,” she wrote in an email that Edwards shared with me. “We’ll go back to doing the work on our own with those willing to work WITH us in the community as we discover more and vindicate what the residents here already know by THE PAIN WE ARE IN, that it is not safe to bathe.”

On a hot May afternoon, Mays and other Flint residents drove to Ann Arbor to protest outside the condominium on Main Street where Gov. Rick Snyder lives when he isn’t in Lansing. They wore bathrobes and carried signs calling for Snyder’s impeachment. “Tricky Ricky, you can’t hide! We can see your dirty side!” the protesters chanted. I spotted a woman in a pink bathrobe and a FLINT LIVES MATTER T-shirt whom Edwards had introduced me to in the winter. Her name was Nayyirah Shariff, and she was a community organizer with the Flint Democracy Defense League. When we first met, Shariff expressed gratitude and admiration for what Virginia Tech had done, but her opinion of Edwards had since changed. “Now it feels like, intentionally or unintentionally, he’s filling the role of the State of Michigan and how they felt about our experiences back in the summer of 2015.”

Photo

The Flint River.Credit
Jeremy M. Lange for The New York Times

When I caught up with Melissa Mays, she said, “What broke my heart the most is that when we brought Marc Edwards in last August, the state did the same thing to him, called him a fear-­monger. That’s the same thing that Marc just did to Water Defense.” Edwards’s remarks about hygiene, moreover, were offensive. People in Flint hadn’t stopped bathing despite their adverse reactions. “You’re saying that we’re dumb and dirty,” Mays said. “That’s what’s wrong with us.”

At the end of May, Edwards returned to Michigan to hold yet another news conference, at which he and other scientists would try to allay the fears and doubts that Water Defense had fueled. For this occasion, Edwards toned down his rhetoric, presenting the latest data neutrally. Lead levels were still too high, but they were coming down. The disinfection byproducts were comparable to the national average. Sounding weary, he continued: “I understand that the trust will never be there for some people. If the residents in Flint, given their journey, decide they never want to drink tap water again, never want to take a bath or shower again, I’m not going to try to talk them out of it, because they went through hell for 18 months.”

After the news conference ended, Edwards visited the home of Mari Copeny, the 9-year-old known as Little Miss Flint, whose letter to President Obama prompted him to visit. From LeeAnne Walters, Edwards had learned that Water Defense had collected samples in Mari’s home. She was at school, but her mother, Lulu Brezzell, let Edwards in. Even after the city returned to Detroit’s system, the water gave her family bad rashes, Brezzell said. She showed him pictures — angry red splotches on hands and arms and legs. Washing the dishes made the skin on her knuckles blister and split. She and her children were still doing their best to practice good hygiene, but they had learned to take “speed showers” — no more than two minutes. Water Defense had found high levels of chloroform in her water. Another scientist, with Hydroviv, a company that sells water filters, told her that her chloroform levels were “comparable to other municipal water sources.” Like many people in Flint, she didn’t know what or whom to believe, but she was inclined to trust her symptoms and her senses. Her water smelled “like a swimming pool,” and it had acquired a mysterious blue tint.

“So I do a lot of work with blue water all over the country,” Edwards said. About 80 percent of blue-­water cases are “natural,” a trick of the light, he explained. In the remaining 20 percent, the tint comes from dissolved copper, and unlike lead, a little copper is harmless. To figure out whether Brezzell’s blue water was natural or chemical, all you had to do was place a bottle of it and a bottle of store-bought water against a white background.

Upstairs in her little bathroom, he filled the tub. As the water rose, it took on a tint. “Can you see it?” Brezzell asked. “Nice and blue?”

She was relieved to hear him say this. “People were saying: ‘You’re crazy. The water’s not blue.’ I’m like, ‘Yes, it is!’ ”

“So now the question, though: Is it bluer than normal water?” Edwards said. He performed his test, filling a bottle from Brezzell’s tub and comparing it with a bottle of store-bought water.

“They’re a different color!” Brezzell said hopefully.

Edwards held the bottles up to a fluorescent light above the sink.

“That is blue water,” Edwards said. “But it’s light blue.” He took the two bottles outside. In natural light, they were harder to distinguish. Compared with other blue water he had studied, on a blueness scale of 1 to 10, hers was low, around a 1.5, he estimated. He meant this to sound reassuring: The 1.5 was close to normal, most likely indicative of a little copper, but nothing to worry about.

“It’s still darker, though,” Brezzell said, and you could tell from the insistence in her voice that she was neither comforted nor convinced.

Edwards was not surprised by her reaction, he later told me. She had horrible rashes and so did her children. She was in pain. “And when you’re in pain, you want an answer, even if it’s wrong,” and he had no firm conclusions to offer, only data and hypotheses. All he knew for certain was what the lab tests eventually told him: that contrary to what Water Defense had told her, the chloroform levels were typical for American cities. The same was true of the disinfection byproducts and copper. Her chlorine levels, though well below the E.P.A. limit, were a bit high. Perhaps this explained the rashes. Perhaps she and her children were sensitive to chlorine. Perhaps a filter for her shower head would help.

Early this month, I spoke to Edwards one last time. A year ago, he was the troublemaking outsider whom the authorities were accusing of “fanning the political flames irresponsibly.” Now he was the authority making that case about others, and if many of the activists now considered him an untrustworthy agent of the state, there was nothing he could do about it. In both roles, he said, he had been the advocate for “sound science.”

“This is what a ‘dark age’ looks like,” he wrote me in an email the morning after our conversation. “When science is no longer a source of enlightenment, people still need to believe in something.” The people of Flint had been betrayed, and the betrayal had pushed some of them “into the anti-­science camp.” He continued: “We lost our authority and the public trust with good reason. After Flint kids were protected, I took off my activist suit and put on my lab coat. Some people assumed my motives could be changed just as easily. Not so, but arguing about it is not productive. Our energies have to be focused on not betraying the public in the first place.”

Correction: August 28, 2016

Picture credits on Aug. 21 with an article about the water crisis in Flint, Mich., omitted the photographer’s middle initial. He is Jeremy M. Lange.

Correction: September 11, 2016

An article on Aug. 21 about the water-contamination crisis in Flint, Mich., described incorrectly a statement the American Association for the Advancement of Science (A.A.A.S.) made on advocacy in science. It was in a paper commissioned for an A.A.A.S. workshop; it was not an official report. And it was commissioned in 2011, not 2016.

Correction: September 4, 2016

An article on Aug. 21 about Flint’s water-contamination crisis referred incorrectly to Scott Smith’s relationship with Water Defense when he was named the group’s chief water scientist. He was appointed to the post and receives no compensation beyond expenses; he was not hired.